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Mount St. Helens

The Volcano That Reshaped Modern Volcanology

Elevation

2,549 m

Last Eruption

2004–2008

Type

Stratovolcano

Country

United States

Location

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Volcanic Hazards & Risk Assessment

Primary Hazards

  • Pyroclastic flows
  • Lava flows
  • Volcanic bombs and ballistics
  • Lahars and mudflows

Risk Level

Population at RiskModerate
Infrastructure RiskHigh
Aviation RiskSignificant

Geological Composition & Structure

Rock Types

Primary
Unknown
Silica Content
Varied composition

Tectonic Setting

Unknown
Intraplate setting with hotspot or regional volcanic activity.

Age & Formation

Epoch
Unknown
Evidence
Unknown

Eruption Statistics & Analysis

MetricValueGlobal RankingSignificance
Total Recorded EruptionsUnknownLowModerately active volcano
Maximum VEIVEI UnknownMinorLocal impact potential
Recent Activity-20039982 years agoVery RecentCurrently active

Monitoring & Alert Status

Monitoring Networks

USGS Volcano Hazards Program
Comprehensive monitoring network
Global Volcanism Program
International eruption database

Current Status

Active
Recent volcanic activity detected. Continuous monitoring in place.

Authority Sources

Smithsonian GVP
Official volcano database
USGS Volcano Hazards
U.S. Geological Survey

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Interesting Facts

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The 1980 eruption triggered the largest debris avalanche ever recorded — 2.5 km³ of material traveling at speeds up to 250 km/h, burying the North Fork Toutle River valley under deposits averaging 46 m deep.

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Mount St. Helens lost 401 m (1,314 ft) of its summit in the 1980 eruption, reducing its height from 2,950 m (9,677 ft) to 2,549 m (8,363 ft) — transforming it from the fifth-tallest Cascade peak to one of the shortest major stratovolcanoes in the range.

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The lateral blast on May 18, 1980 traveled at speeds exceeding 1,080 km/h (670 mph) — faster than the speed of sound — and flattened approximately 4 billion board feet of timber across 600 km².

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Before 1980, Mount St. Helens was sometimes called 'the Fujisan of America' for its symmetrical, snow-capped cone — a resemblance now completely erased.

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The 1980 eruption's thermal energy was equivalent to approximately 24 megatons of TNT — roughly 1,600 times the energy of the Hiroshima atomic bomb.

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Spirit Lake's surface elevation rose approximately 60 m (200 ft) during the 1980 debris avalanche, and the lake initially contained an estimated 1 million floating logs — a log mat that persisted for years.

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Mount St. Helens is the youngest major stratovolcano in the Cascades, with its current edifice only about 40,000–50,000 years old, while neighboring Rainier is approximately 500,000 years old.

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The eruption killed 57 people, including USGS volcanologist David A. Johnston, whose final radio message — 'Vancouver! Vancouver! This is it!' — has become one of the most quoted statements in geological history.

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A new glacier, Crater Glacier, began forming inside the crater in the mid-1990s and is one of the youngest glaciers on Earth. By 2004 it had split into two arms flowing around the growing lava dome.

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The 2004–2008 dome-building eruption extruded a remarkable 'lava spine' — a solid plug of rock pushed upward at 1–2 m per day — the fastest-growing such feature ever documented.

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Mount St. Helens has produced 44 recorded eruptions in the Holocene — more than any other volcano in the Cascade Range, including Rainier (20), Shasta (22), and Baker (11).

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The Ape Cave lava tube on the volcano's south flank, formed about 2,000 years ago, is one of the longest lava tubes in the contiguous United States at 3.9 km (2.4 mi).

Frequently Asked Questions

Is Mount St. Helens still active?
Yes, Mount St. Helens is classified as an active volcano by the United States Geological Survey (USGS). Its most recent eruption was a dome-building episode from 2004 to 2008, during which new lava was extruded into the crater formed by the catastrophic 1980 eruption. The volcano is continuously monitored by the USGS Cascades Volcano Observatory using a dense network of seismometers, GPS instruments, gas sensors, and cameras. Low-level seismic activity occurs continuously beneath the volcano, indicating that magma systems remain active at depth. Volcanologists consider future eruptions to be a certainty — St. Helens has been the most active Cascade volcano throughout the Holocene, with 44 recorded eruptions and average repose intervals of less than 100 years between eruptive periods.
When did Mount St. Helens last erupt?
Mount St. Helens' most recent eruption was a dome-building episode that began on October 1, 2004 and continued until January 2008. This eruption was largely effusive (non-explosive), extruding thick dacite lava into the horseshoe-shaped crater at rates initially exceeding 5 cubic meters per second. It added approximately 125 million cubic meters of new material to the crater dome. Prior to this, the volcano's most famous eruption occurred on May 18, 1980 — a catastrophic VEI 5 event that killed 57 people, produced the largest debris avalanche ever recorded, and blew away the upper 400 m of the mountain. Between 1980 and 2004, smaller eruptions occurred in 1989–1990 and 1990–1991.
Could Mount St. Helens erupt again?
Mount St. Helens will almost certainly erupt again. The volcano has been the most active in the Cascade Range throughout the Holocene, with 44 documented eruptions over the past 4,300 years and an average interval of less than 100 years between eruptive periods. The USGS classifies it as one of the highest-threat volcanoes in the United States. Future eruptions could range from relatively mild dome-building episodes similar to 2004–2008 to explosive Plinian events comparable to or larger than 1980. The volcano's geological record includes a VEI 6 eruption around 1860 BCE — ten times more powerful than the 1980 event. The USGS Cascades Volcano Observatory monitors St. Helens continuously and would likely detect precursory signs weeks to months before a significant eruption.
How many people died in the 1980 eruption?
Fifty-seven people were killed in the May 18, 1980 eruption of Mount St. Helens. Most victims were outside the restricted zone that had been established around the volcano but within the blast zone that proved far larger than anticipated. Causes of death included asphyxiation from inhaling hot ash and gases, thermal injuries from the superheated lateral blast (temperatures exceeding 360°C), and burial by the debris avalanche. Among the victims was David A. Johnston, a 30-year-old USGS volcanologist stationed at an observation post 10 km from the summit, and Harry R. Truman, an 83-year-old lodge owner who had refused to evacuate from his home at Spirit Lake. The death toll would have been far higher if the eruption had not occurred on a Sunday morning, when logging operations in the surrounding forests were idle.
How tall is Mount St. Helens?
Mount St. Helens currently stands at 2,549 m (8,363 ft) above sea level. Before the catastrophic eruption of May 18, 1980, the volcano's summit elevation was 2,950 m (9,677 ft) — making it the fifth-tallest peak in Washington State. The eruption removed the top 401 m (1,314 ft) of the mountain, including the entire summit dome, through a combination of the debris avalanche and explosive ejection. By comparison, neighboring Mount Rainier reaches 4,392 m (14,411 ft), Mount Adams stands at 3,742 m (12,276 ft), and Mount Hood in Oregon rises to 3,426 m (11,239 ft). Lava dome growth since 1980 has partially filled the crater but has not significantly increased the volcano's summit elevation.
What type of volcano is Mount St. Helens?
Mount St. Helens is a stratovolcano, also known as a composite volcano. Stratovolcanoes are built from alternating layers of lava flows, volcanic ash, pumice, and other pyroclastic deposits, forming steep-sided, roughly conical mountains. St. Helens' dominant magma composition is dacite — a silica-rich, viscous magma type that traps dissolved gases and produces highly explosive eruptions. This composition is characteristic of subduction-zone volcanoes worldwide. Stratovolcanoes are the most common type of volcano along the Ring of Fire and include some of the world's most dangerous volcanic peaks, including Mount Vesuvius, Mount Pinatubo, and Mount Fuji. St. Helens' eruption styles have ranged from effusive dome-building to catastrophic Plinian explosions, reflecting the full spectrum of stratovolcano behavior.
Can you visit Mount St. Helens?
Yes, Mount St. Helens is open to visitors year-round as part of the Mount St. Helens National Volcanic Monument, managed by the U.S. Forest Service. The Johnston Ridge Observatory, located 8 km from the crater, is the premier visitor destination and is typically open mid-May through October. Climbing to the crater rim is permitted with a permit (required May 15–October 31, limited to approximately 100 climbers per day, available online or at the trailhead) via the Monitor Ridge route, a strenuous 14.5 km round trip taking 7–12 hours. Other popular attractions include the Ape Cave lava tube, the Boundary Trail through the blast zone, and the Windy Ridge viewpoint overlooking Spirit Lake. Winter visitors can snowshoe or backcountry ski on the lower flanks.
What caused the 1980 eruption of Mount St. Helens?
The 1980 eruption was caused by the intrusion of magma into the volcano's interior, which destabilized the north flank over a period of weeks. Beginning in mid-March 1980, a series of earthquakes indicated that magma was rising beneath the mountain. A large bulge developed on the north face, expanding outward at rates of up to 2.5 m (8 ft) per day. On May 18, a magnitude 5.1 earthquake triggered the collapse of this over-steepened flank in a massive debris avalanche, which instantaneously depressurized the magma system beneath. The sudden release of pressure caused the superheated magma and gases to explode laterally in a devastating blast. The underlying cause is the subduction of the Juan de Fuca Plate beneath North America, which generates magma that feeds all Cascade volcanoes.
What would happen if Mount St. Helens erupted today?
A future eruption of Mount St. Helens could range from a relatively minor dome-building event (similar to 2004–2008) to an explosive eruption comparable to or larger than 1980. In a worst-case VEI 5+ scenario, pyroclastic flows could sweep down the flanks at speeds exceeding 160 km/h, lahars could travel down the Toutle and Cowlitz river valleys toward communities including Castle Rock, Longview, and Kelso (threatening approximately 50,000 people), and ash could blanket communities across the Pacific Northwest. Portland, Oregon (80 km south) could receive significant ashfall. However, the USGS Cascades Volcano Observatory maintains continuous monitoring and would likely provide days to weeks of warning before a major eruption, enabling evacuations. The 2004–2008 eruption demonstrated that modern monitoring can successfully manage eruption risk.
How does Mount St. Helens compare to Mount Rainier?
Mount St. Helens and Mount Rainier are both active Cascade stratovolcanoes, but they differ significantly in size, hazard profile, and eruptive history. Rainier (4,392 m) is nearly twice the height of post-1980 St. Helens (2,549 m) and carries 25 major glaciers containing over 4 km³ of ice — the largest glacial system on any volcano in the contiguous United States. This ice mass means Rainier's greatest hazard is lahars, which could reach the Puget Sound lowlands and communities of over 100,000 people. St. Helens, by contrast, has been far more active: 44 eruptions versus Rainier's 20, with a maximum VEI of 6 versus Rainier's 4. St. Helens has more explosive potential, while Rainier poses a greater lahar threat due to its massive ice cover and proximity to denser populations.